Over the past several years, the market for optical communications systems has grown significantly. Two types of cables generally are used in optical communications. One includes a plurality of lightguide fibers which are arranged in ribbons and in arrays or stranded together, and another which is a single lightguide fiber. The single lightguide fiber cables have been used to interface electrical and optical apparatus such as, for example, regenerators and signal coders and to provide optical patch cords and jumper cables for main distributing frames.
Each of the above-described cables has its own connection technology. In making a single, fiber-to-fiber connection, end portions of the two lightguide fibers to be spliced together must be aligned coaxially such that end faces of the opposing fibers are in a predetermined relationship to each other. This is important, particularly since signal losses which are introduced by axial misalignment and end separation are synergistically cumulative.
A single fiber lightguide connector may be one such as that shown on pages 89-90 of an article by T. L. Williford et al entitled "Interconnection for Lightguide Fibers" published in the Winter 1980 issue of the Western Electric Engineer. The basic elements of the connector are a plastic conical plug which is molded about the end of the fiber with the fiber centered inside the plug, and a biconical sleeve which accepts two plugs and causes the alignment of the axes of the fiber ends. The biconical alignment sleeve is a precisely molded part. It includes two truncated conical cavities that control the end separation and axial alignment of the end faces of the fibers which are encapsulated within the plugs that are seated in the conical cavities of the sleeve. The circular symmetry of the conical design provides precise axial alignment of the lightguide fiber cores.
Interconnection requires that the ends of the lightguide fibers be smooth, flat and perpendicular to the lightguide fiber axes and the lightguide fiber axes to be coincident with those of the plugs and the biconical alignment sleeve. Also, each plug must be sized precisely to control plug end separation within the biconical alignment sleeve. When the plug is molded about the fiber, a portion of the fiber extends beyond an end face of the plug.
To obtain the required end separation and geometry of the end faces of the opposing fibers when connectorized, it becomes necessary to sever the extending end portion of the fiber and to grind, then polish the end faces of the fiber and plug to a tolerance of about 0 to 0.00150 cm. A technique for the first stage of a single fiber end preparation in which the extending portion of the fiber is removed and the end faces of the plug and fiber abraided is described in U.S. Pat. No. 4,384,431 which issued on May 24, 1983 in the name of K. W. Jackson.
Presently, the final polishing is accomplished by moving the plug into seating engagement with the wall of a tapered opening of an insert in a metal disc. An end of the plug which is to be polished extends beyond the disc. The disc is moved in an oscillatory manner in a slurry or on a pad which is coated with aluminum oxide. The plug is held manually in the insert as the disc is being moved.
This procedure presents several problems. First, the disc which is made of steel wears as it is moved about in the polishing medium. As a result, the distance between the end of the plug and the disc changes. This causes an excessive gap between ends of the fibers when two plugs are mounted in a biconical connector sleeve. Also, since the plug is held by hand in the insert, it tends to wobble. This often results in a non-flat plug end which does not satisfy the requirement of flatness within 0.00000025 micron. If the plug wobbles, it is unlikely that the end face will be perpendicular to the fiber. Lastly, when the plug is mounted in a biconical connector sleeve, a compression spring applies a predetermined force to the plug. If this same force is not applied to the plug during polishing, the plug may occupy a different position with respect to the insert than with respect to the sleeve.
There is still a need for methods and apparatus for the rapid final preparation of terminated lightguide fiber ends in a repetitively controllable fashion to facilitate the factory and/or field connectorization of single fiber lightguide cables. This need is not met by any known apparatus and while presently used techniques may be used, the elements of control and speed are lacking. Seemingly, the prior art does not include methods and apparatus for polishing an end of a plug through which a lightguide fiber extends and for causing the plug to be held during polishing in a manner similar to that in which it will be held in a biconical sleeve.